On Performance Debugging of Unnecessary Lock Contentions on Multicore Processors: A Replay-based Approach

Locks have been widely used as an effective synchroniza-tion mechanism among processes and threads. However, we observe that a large number of false inter-thread depen-dencies (i.e., unnecessary lock contentions) exist during the program execution on multicore processors, thereby incur-ring significant performance overhead. This paper presents a performance debugging framework, PERFPLAY, to facil-itate a comprehensive and in-depth understanding of the performance impact of unnecessary lock contentions. The core technique of our debugging framework is trace re-play. Specifically, PERFPLAY records the program execution trace, on the basis of which the unnecessary lock contentions can be identified through trace analysis. We then propose a novel technique of trace transformation to transform these identified unnecessary lock contentions in the original trace into the correct pattern as a new trace free of unnecessary lock contentions. Through replaying both traces, PERFPLAY can quantify the performance impact of unnecessary lock contentions. To demonstrate the effectiveness of our de-bugging framework, we study five real-world programs and PARSEC benchmarks. Our experimental results demonstrate the significant performance overhead of unnecessary lock contentions, and the effectiveness of PERFPLAY in identify-ing the performance critical unnecessary lock contentions in real applications. 1